Air-purifying respirators are worn on a user's face for protection against gases, vapors and particulates. They filter the air breathed by a user to remove the noxious gases, vapors and particulates while enabling oxygen in the atmosphere to reach the user. An air-purifying respirator typically consists of three parts: a facepiece, a filter, and a head harness. The facepiece can be a full mask, covering the entire face and forming a seal therewith; or it can be a half-mask, covering only the nose and mouth and forming a seal there-around. The head harness typically consists of a yoke with straps attached thereto. The yoke is attached to the facepiece such that when the straps are worn, the head harness keeps the facepiece sealed against the face. The filter is connected to the facepiece and removes the noxious substances from the air as it is inhaled into the facepiece. The facepiece also often includes an exhalation valve which permits expired air to be vented directly to the outside of the facepiece, but which remains closed during inhalation so that all inhaled air passes through the filter. Examples of typical air-purifying respirators are the Advantage.RTM. 200 half-mask respirator and the Advantage.RTM. 1000 full-mask respirator made by Mine Safety Appliances Company ("MSA") of Pittsburgh, Pa. and described in MSA Data Sheet No. 10-00-05 (1998) and MSA Bulletin No. 1012-06 (1998). The Advantage.RTM. 200 respirator is also shown and described in U.S. Pat. No. 5,592,937.
Respirator filters come in various shapes, sizes and materials. Some are in the form of rigid cartridges, such as disclosed in U.S. Pat. No. 5,714,126. Some are in the form of flexible filter pads, such as disclosed in U.S. Pat. No. Re. 35,062. Other's are somewhere in between such as the filter pad with a rigid perimeter such as disclosed in U.S. Pat. No. 5,732,695. These filters are the result of trade-offs between competing design considerations such as increased efficiency, lower breathing resistance and durability.
For example, in U.S. Pat. No. Re. 35,062, the filter consists of two filter pads secured along their outer edges to face in opposing directions. The filter pads are separated by a porous layer which forms an interior region in which the air may be drawn through the filter pads. A connector is provided through one of the pads to connect this interior region with the inlet valve of the respirator facepiece. As the user inhales, air is drawn through the surfaces of both filter pads into the porous layer and then through the connector into the facepiece via the inlet valve.
While this two-pad design is useful in reducing breathing resistance without significantly detracting from filtration efficiency, a need remains in the art to develop even better designs having improved performance and use characteristics. For instance, this flexible, pad-type filter is generally secured to and disconnected from the respirator facepiece by attaching the connector to the respirator using a threaded or bayonet-type fitting. In doing so, the user must grasp and touch the filter pads and twist or otherwise manipulate the filter to make the connection. This means that any soil on the user's hands can contaminate the filter pad thus reducing filtration efficiency. Moreover, in twisting or otherwise manipulating the filter pad for connection or disconnection with the respirator facepiece, the pliable filter material tends to be rotated or turned further than the relatively stiff connector to which it is attached, thereby placing stress on the filter material surrounding the connector. This relative rotational stress on the filter material can potentially lead to tearing or other damage of the material and possibly even separation of the filter material from the connector.
From the above it is clear that minimizing and even preventing user contact with the filter material, preventing bending of the filter material during removal and attachment, and preventing relative rotation between the filtration material and the connector are desirable objectives to enhance the overall performance and durability of a flexible pad-type filter. Of course, it is still necessary to maintain filtration efficiency while reducing breathing resistance, preferably by to increasing the overall filtering surface area while making the filter relatively compact so as not to obstruct the user's view or otherwise frustrate the user's ability to work when wearing the respirator.
The filter shown in U.S. Pat. No. 5,732,695 uses an internal rigid frame with an outer peripheral band to keep the filter pads separate and to overcome some of the problems discussed above with regard to preventing bending of the filter material during removal and attachment and preventing the relative rotation between the filter material and the connector. In doing so, however, this filter is no longer flexible, but is rigid.
It would be very desirable to overcome the attachment and rotation problems described above without having to sacrifice the flexibility of the pad-type filter. A flexible or deformable filter is a very desirable feature, especially since such a filter can easily fit under a welding shield by conforming to the shape of the shield as it is raised and lowered.